In recent years, liquid crystal display devices, which are thin and light in weight, have been used as personal computer displays and PDA (personal digital assistance) displays. However, conventional twist nematic (TN) type and super twist nematic (STN) type liquid crystal display devices have a narrow viewing angle. Various technical developments have been undertaken to solve the problem.
A typical technique for improving the viewing angle characteristic of a TN or STN type liquid crystal display device is to add an optical compensation plate(s) thereto. Another approach is to employ a transverse electric field mode in which a horizontal electric field with respect to the substrate plane is applied across the liquid crystal layer. Transverse electric field mode liquid crystal display devices have been attracting public attention and have been mass-produced in recent years. Still another technique is to employ a DAP (deformation of vertical aligned phase) mode in which a nematic liquid crystal material having a negative dielectric anisotropy is used as a liquid crystal material and a vertical alignment film is used as an alignment film. This is a type of ECB (electrically controlled birefringence) mode, in which the transmittance is controlled by using the birefringence of liquid crystal molecules.
While the transverse electric field mode is an effective approach to improve the viewing angle, the production process thereof imposes a significantly lower production margin than that of a normal TN type device, whereby it is difficult to realize stable production of the device. This is because the display brightness or the contrast ratio is significantly influenced by variations in the gap between the substrates or a shift in the direction of the transmission axis (polarization axis) of a polarization plate with respect to the orientation axis of the liquid crystal molecules. It requires further technical developments to be able to precisely control these factors and thus to realize stable production of the device.
In order to realize a uniform display without display non-uniformity with a DAP mode liquid crystal display device, an alignment control is often necessary. An alignment control can be provided by, for example, subjecting the surface of an alignment film to an alignment treatment by rubbing. However, when a vertical alignment film is subjected to a rubbing treatment, rubbing streaks are likely to appear in the displayed image, and it is typically not suitable for mass-production.
In view of this, there has been proposed in the art another approach wherein a predetermined electrode structure including openings and a solid portion is employed for one of a pair of electrodes opposing each other via the liquid crystal layer therebetween, so that a plurality of liquid crystal domains each taking a radially-inclined orientation are formed in the openings and the solid portion each by an inclined electric field produced at an edge portion of the opening (e.g., see Japanese Laid-Open Patent Publication No. 2003-043525). With this approach, a liquid crystal domain having a radially-inclined orientation can be formed stably and with a high degree of continuity, thereby improving viewing angle characteristics and display quality.
However, as liquid crystal display devices are becoming more and more widespread, display characteristic requirements for a liquid crystal display device have been increasing, and there has been a demand for further improvements in display characteristics such as the display brightness and the response speed.